Fluctuation driven transitions in localized insulators: Intermittent metallicity and path chaos precede delocalization

TL;DR

This paper investigates how slow thermal fluctuations influence the transition from localized insulators to metallic phases, revealing multiple phases and transitions, including intermittent metallicity and path chaos, with implications for understanding delocalization.

Contribution

It introduces a detailed analysis of fluctuation-driven transitions in localized insulators, identifying new phases and the role of thermal fluctuations in delocalization.

Findings

Three distinct insulating phases identified

Intermittent metal phase characterized by rare but strong fluctuations

Transition to a phase with fluctuating paths near delocalization

Abstract

We study how interacting localized degrees of freedom are affected by slow thermal fluctuations that change the effective local disorder. We compute the time-averaged (annealed) conductance in the insulating regime and find three distinct insulating phases, separated by two transitions. The first occurs between a non-resonating insulator and an intermittent metal. The average conductance is always dominated by rare temporal fluctuations. However, in the intermittent metal, they are so strong that the system becomes metallic for an exponentially small fraction of the time. A second transition occurs within that phase. At stronger disorder, there is a single optimal path providing the dominant contribution to the conductance at all times, but closer to delocalization, a transition to a phase with fluctuating paths occurs. This last phase displays the quantum analogon of configurational chaos in glassy systems in that thermal fluctuations induce significant changes of the dominant decay channels. While in the insulator the annealed conductance is strictly bigger than the conductance with typical, frozen disorder, we show that the threshold to delocalization is insensitive to whether or not thermal fluctuations are admitted. This rules out a potential bistability, at fixed disorder, of a localized phase with suppressed internal fluctuations and a delocalized, internally fluctuating phase.